Protection film having base layer over adhesive layer

ABSTRACT

A protection film for an electronic device includes an adhesive layer including a first surface to which an electronic device is attached, and a film layer which contacts a second surface of the adhesive layer and includes at least one member, where a thickness of the adhesive layer satisfies Inequality 1:z≤(5.1x+57.4)·ln(y)−(14.7x+140.5),where z is the thickness of the adhesive layer in terms of micrometers, x is a modulus of a member of the film layer which directly contacts the adhesive layer in terms of gigapascals, and y is a total thickness of the film layer in terms of micrometers.

This application is a continuation of U.S. patent application Ser. No.16/843,458, filed on Apr. 8, 2020, which claims priority to U.S. patentapplication Ser. No. 16/396,421, filed on Apr. 26, 2019, which claimspriority to Korean Patent Application No. 10-2018-0112073, filed on Sep.19, 2018, and all the benefits accruing therefrom under 35 U.S.C. § 119,the content of which in its entirety is herein incorporated byreference.

BACKGROUND 1. Field

Exemplary embodiments of the invention relate to a protection film andan electronic device including the same.

2. Description of the Related Art

With an increasing demand for small electronic devices such as smartphones, bendable or foldable electronic devices are being launched formore various applications.

To prevent a damage to a surface of an electronic device as much aspossible, a protection film is desired to have high durability. Thus,the protection film is formed to have a rigid property.

SUMMARY

Since an electronic device is repeatedly bent or folded and thenunfolded during a use, a protection film is easily deformed, or crackingor whitening occurs frequently.

Exemplary embodiments of the invention provide a protection film whichhas excellent durability for a long period of time even when anelectronic device is repeatedly bent or folded and then unfolded andprotects a body of the electronic device from external impacts and anelectronic device to which the protection film is applied.

However, the invention is not restricted to the one set forth herein.The above and other exemplary embodiments of the invention will becomemore apparent to one of ordinary skill in the art to which the inventionpertains by referencing the detailed description of the invention givenbelow.

According to an exemplary embodiment of the invention, there is provideda protection film for an electronic device. The protection film for anelectronic device includes an adhesive layer including a first surfaceto which an electronic device is attached, and a film layer whichcontacts a second surface of the adhesive layer and includes at leastone member, where the thickness of the adhesive layer satisfiesInequality 1: z≤(5.1x+57.4)·ln(y)−(14.7x+140.5) where z is a thicknessof the adhesive layer in terms of micrometers, x is a modulus of amember of the film layer which directly contacts the adhesive layer interms of gigapascals, and y is a total thickness of the film layer interms of micrometers.

According to another exemplary embodiment of the invention, there isprovided an electronic device. The electronic device includes a bodywhich includes at least one member; and a protection film which isattached onto at least a portion of a surface of the body, where theprotection film includes an adhesive layer which includes a firstsurface attached to the surface of the body and a film layer whichcontacts a second surface of the adhesive layer and includes at leastone member, and a thickness of the adhesive layer satisfies Inequality2: z≤(5.1x+57.4)·ln(y)−(14.7x+140.5), where z is the thickness of theadhesive layer in terms of micrometers, x is a modulus of a member ofthe film layer which directly contacts the adhesive layer in terms ofgigapascals, and y is a total thickness of the film layer in terms ofmicrometers.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other exemplary embodiments will become apparent and morereadily appreciated from the following description of the exemplaryembodiments, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a cross-sectional view of an exemplary embodiment of aprotection film;

FIG. 2 is a cross-sectional view of the protection film of FIG. 1 in afolded state;

FIG. 3 is a cross-sectional view illustrating the protection film ofFIG. 1 attached to an organic light emitting display device;

FIG. 4 is a cross-sectional view illustrating a process in which theorganic light emitting display device to which the protection film of inFIG. 1 has been attached is folded;

FIG. 5 is a cross-sectional view illustrating a process in which theorganic light emitting display device to which the protection film ofFIG. 1 has been attached is unfolded;

FIG. 6 is a graph illustrating the amount of tensile stress according tothe strain of an adhesive layer in an A region when the processes ofFIGS. 4 and 5 are repeated;

FIG. 7 is a graph illustrating the strain of the adhesive layeraccording to the thickness of the adhesive layer for each thickness of abase layer;

FIG. 8 is a cross-sectional view illustrating, as a comparative example,a folded protection film to which an adhesive layer having a thicknessexceeding a maximum usable thickness has been applied;

FIG. 9 is a cross-sectional view of an exemplary embodiment of aprotection film; and

FIG. 10 is a cross-sectional view of an exemplary embodiment of aprotection film.

DETAILED DESCRIPTION

Features of the invention and methods of accomplishing the same may beunderstood more readily by reference to the following detaileddescription of embodiments and the accompanying drawings. The inventionmay, however, be embodied in many different forms and should not beconstrued as being limited to the exemplary embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete and will fully convey the concept of theinventive concept to those skilled in the art, and the invention willonly be defined by the appended claims.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on”, “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother region, layer or section. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “Or” means “and/or.” As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower,” can therefore, encompasses both an orientation of “lower” and“upper,” depending on the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±30%, 20%, 10%, 5% of the stated value.

An electronic device may be provided as it is, but may also be providedwith a protection film attached to at least a portion of the surface ofits body to prevent the body from being damaged by an external impact.The electronic device may be, for example, an electronic productincluding a display panel, such as a smart phone, a tablet computer, amobile phone, a video phone, an electronic book reader, a desktopcomputer, a laptop computer, a netbook computer, a workstation, aserver, a personal digital assistant (“PDA”), a portable multimediaplayer (“PMP”), an MP3 player, a mobile medical device, a camera, or awearable device. In an alternative exemplary embodiment, the electronicdevice may be a home appliance such as a television, a digital videodisk (“DVD”) player, an audio player, a refrigerator, an airconditioner, a vacuum cleaner, an oven, a microwave oven, a washingmachine, an air purifier, a set-top box, a home automation controlpanel, a security control panel, a television (“TV”) box, a gameconsole, an electronic dictionary, an electronic key, a camcorder, or anelectronic picture frame. In an alternative exemplary embodiment, theelectronic device may be a medical device (such as various portablemedical measuring instruments (including a glucose meter, a heart ratemonitor, a blood pressure monitor and a body thermometer), a magneticresonance angiography (“MRA”) device, a magnetic resonance imaging(“MRI”) device, a computed tomography (“CT”) device, an imaging deviceor an ultrasonic device), a navigation device, a global navigationsatellite system (“GNSS”), an event data recorder (“EDR”), a flight datarecorder (“FDR”), an automotive infotainment device, marine electronicequipment (such as a marine navigation device or a gyrocompass),avionics, a security device, an automotive head unit, an industrial orhome robot, an automatic teller's machine (“ATM”), a point of sales(“POS”) terminal of a shop, or an Internet-of-things (“IoT”) device(such as an electric bulb, various sensors, an electric or gas meter, asprinkler, a fire alarm, a thermostat, a street lamp, a toaster,exercise equipment, a hot water tank, a heater or a boiler).

In various embodiments, the electronic device may be a combination ofone or more of the various devices described above. The electronicdevice according to an exemplary embodiment may be a flexible electronicdevice or a foldable electronic device.

For ease of description, a foldable organic light emitting displaydevice will be described herein as an example of the electronic device.

A foldable display device may refer to a display device that can berepeatedly folded and unfolded easily regardless of the shape of a panelor a display device that includes two or more panels connected by acoupling medium and can be folded or unfolded using the coupling mediumeven if the panels themselves cannot be easily folded and unfolded.

The foldable display device may be a liquid crystal display device, aplasma display device, an electrophoretic display device or anelectrowetting display device, in addition to the organic light emittingdisplay device mentioned above.

An electronic device according to an exemplary embodiment of thedocument is not limited to the organic light emitting display device andthe above-mentioned devices and may also be a novel electronic deviceintroduced according to technological development.

Hereinafter, embodiments of the disclosure will be described in detailwith reference to the accompanying drawings. The same or similarreference numerals are used for the same elements in the drawings. Inthe drawings, thicknesses are enlarged to clearly indicate layers andregions. In addition, for ease of description, the thicknesses of somelayers and regions are exaggerated in the drawings.

FIG. 1 is a cross-sectional view of a protection film 10 according to anexemplary embodiment. FIG. 2 is a cross-sectional view of the protectionfilm 10 of FIG. 1 in a folded state. FIG. 3 is a cross-sectional viewillustrating the protection film 10 of FIG. 1 attached to an organiclight emitting display device 20.

Referring to FIGS. 1 through 3 , the protection film 10 is attached ontoa surface of the organic light emitting display device 20. Although notillustrated in the drawings, the protection film 10 may also be attachedto cover a portion of the organic light emitting display device 20 whichincludes not only the surface of the organic light emitting displaydevice 20 but also side edges of the surface. The protection film 10includes a base layer 120 and an adhesive layer 110 disposed on asurface of the base layer 120.

The base layer 120 may be a layer that substantially protects theorganic light emitting display device 20 when the protection film 10 isattached to the organic light emitting display device 20. In anexemplary embodiment, the base layer 120 may include at least one ofpolyethylene terephthalate (“PET”), polyethylene naphthalate (“PEN”),polycarbonate (“PC”), polymethyl methacrylate (“PMMA”), polystyrene,polyvinylchloride, polyethersulfone (“PES”), polyethylene,polypropylene, TRF film, and combinations of these materials, forexample.

In an exemplary embodiment, the thickness of the base layer 120 may beabout 20 micrometers (μm) or more. In an exemplary embodiment, thethickness of the base layer 120 may be about 25 μm to about 75 μm, forexample. By having a thickness within the above range, the base layer120 may fully protect the surface of the organic light emitting displaydevice 20 without excessively increasing the total thickness of theprotection film 10.

The adhesive layer 110 is disposed on a surface of the base layer 120. Asurface of the adhesive layer 110 may be an adhesive surface to beattached to the organic light emitting display device 20. The othersurface of the adhesive layer 110 may be in contact with the surface ofthe base layer 120. When the protection film 10 is attached to theorganic light emitting display device 20, the adhesive layer 110 maydirectly contact the organic light emitting display device 20. Theadhesive layer 110 disposed between the base layer 120 and the organiclight emitting display device 20 includes the function of attaching thebase layer 120 to the organic light emitting display device 20. In anexemplary embodiment, the adhesive layer 110 may be provided using anoptically clear adhesive (“OCA”) such as an acrylic-based adhesive, asilicone-based adhesive, a urethane-based adhesive, a rubber-basedadhesive or a vinyl ether-based adhesive or may be provided using apressure sensitive adhesive (“PSA”), for example. In an exemplaryembodiment, the adhesive layer 110 may include a PSA having a modulus of10 megapascals (MPa) or less at a temperature of −20 degrees Celsius (°C.) or lower.

The adhesive layer 110 may include a first region 110 a wherecompressive stress is generated inside the protection film 10 when theprotection film 10 is bent and a second region 110 b where tensilestress is generated inside the protection film 10 when the protectionfilm 10 is bent. In an exemplary embodiment, when the protection film 10is attached to a light emitting surface of the organic light emittingdisplay device 20 and the organic light emitting display device 20 towhich the protection film 10 has been attached is bent with the lightemitting surface facing inward, compressive stress may be generated inthe first region 110 a of the adhesive layer 110 which is relativelyclose to the base layer 120, and tensile stress may be generated in thesecond region 110 b of the adhesive layer 110 which is relatively closeto the organic light emitting display device 20, for example.

In the drawings, a boundary between tensile stress and compressivestress generated in the adhesive layer 110 is illustrated as being amidway point between a surface where the adhesive layer 110 contacts thebase layer 120 and a surface where the adhesive layer 110 contacts theorganic light emitting display device 20. However, the invention is notlimited thereto. Depending on the material of the adhesive layer 110,the boundary between the tensile stress and the compressive stress maybe provided at a position relatively closer to the surface where theadhesive layer 110 contacts the organic light emitting display device 20than to the surface where the adhesive layer 110 contacts the base layer120 or may be provided at a position relatively closer to the surfacewhere the adhesive layer 110 contacts the base layer 120 than to thesurface where the adhesive layer 110 contacts the organic light emittingdisplay device 20. That is, the thicknesses of the first region 110 aand the second region 110 b in the adhesive layer 110 may be the same,the thickness of the first region 110 a may be relatively greater thanthe thickness of the second region 110 b, or the thickness of the secondregion 110 b may be relatively greater than the thickness of the firstregion 110 a.

The magnitude of compressive stress in the first region 110 a may varyfrom position to position. The compressive stress may be larger as aposition is closer to a relatively bent region (e.g., an A region) inthe first region 110 a. Similarly, the magnitude of tensile stress inthe second region 110 b may vary from position to position. The tensilestress may be larger as a position is closer to the relatively bentregion in the second region 110 b.

When the protection film 10 is bent by applying an external force suchthat the radius of curvature of the second region 110 b is larger thanthat of the first region 110 a as illustrated in FIG. 2 , tensile stressmay act outside the first region 110 a, and compressive stress may actoutside the second region 110 b. Therefore, when the protection film 10is bent as illustrated in FIG. 2 , side surfaces of the adhesive layer110 may be inclined. That is, when the protection film 10 is bent asillustrated in FIG. 2 , the adhesive layer 110 may be reduced in lengthfrom the first region 110 a toward the second region 110 b due to anexternal force. Here, since a restoring force is generated inside theadhesive layer 110, compressive stress may be generated inside the firstregion 110 a whose length has been increased compared with that beforethe application of the external force, and tensile stress may begenerated inside the second region 110 b whose length has been reducedcompared with that before the application of the external force.

The adhesive layer 110 of the protection film 10 according to theillustrated exemplary embodiment has a thickness equal to or smallerthan a maximum usable thickness. Thus, buckling may not occur even whenthe protection film 10 is repeatedly folded and unfolded more than 1000times. The maximum usable thickness of the adhesive layer 110 will bedescribed in detail later.

In an exemplary embodiment, the protection film 10 may have a lighttransmittance of about 90 percent (%) or more and a haze of about 1% orless, specifically, a light transmittance of about 91% to about 95% anda haze of about 0.5% to about 0.8%. The protection film 10 may exhibitexcellent optical properties by having a light transmittance and a hazewithin the above ranges. In an exemplary embodiment, the lighttransmittance may be a value measured according to the conditions of ISO13468, and the haze may be a value measured according to the conditionsof ISO 14782, for example.

In an exemplary embodiment, the base layer 120 of the protection film 10may have a modulus of about 2 gigapascals (GPa) to about 9 GPa accordingto the conditions of ASTM D638, for example. By having a modulus withinthe above range, the base layer 120 may exhibit both sufficientdurability and excellent flexibility. In an exemplary embodiment, thebase layer 120 may have a modulus of about 2 GPa to about 9 GPa evenunder a temperature condition of about −40° C. to about 80° C.

More specifically, when the modulus of the base layer 120 is less thanabout 2 GPa, the protection film 10 may be easily deformed permanently.When the modulus of the base layer 120 is more than about 9 GPa,fissures or cracks may be easily provided in the protection film 10 dueto bending or the like.

As described above, the protection film 10 may have excellent opticalproperties, sufficient durability, and excellent flexibility. Also, evenwhen the protection film 10 is applied to a substrate 210 (including,e.g., a transparent plastic material) of the organic light emittingdisplay device 20, its improved flexibility may prevent breakage orformation of bright dots. Therefore, even when scratches are temporarilygenerated on the surface of the protection film 10, the surface of theprotection film 10 may be restored to its original shape over time dueto its elasticity to resist external stimulation or friction.

As a result, since the properties of the protection film 10 are noteasily deteriorated despite continuous use, the protection film 10 maymaintain excellent optical properties and excellent durability for along time.

When the base layer 120 of the protection film 10 applied to the organiclight emitting display device 20 has a thickness y1, the maximum usablethickness of the adhesive layer 110 may be z1. The thickness of the baselayer 120 and the thickness of the adhesive layer 110 will be describedlater, together with their relationship with the modulus of the baselayer 120.

Next, the organic light emitting display device 20 to which theprotection film 10 may be attached will be described.

Referring to FIG. 3 , the organic light emitting display device 20 mayinclude the substrate 210, an organic light emitting element layer 220disposed on the substrate 210, an encapsulation layer 230 disposed onthe organic light emitting element layer 220, a touch sensing layer 240disposed on the encapsulation layer 230, and a cover window 250 disposedon the touch sensing layer 240.

The substrate 210 may be a flexible display substrate. The flexibledisplay substrate is characterized by including a flexible material thatmay be bent or folded. In an exemplary embodiment, the flexible displaysubstrate may include a plastic film such as a polyimide film or mayinclude sheet glass or a thin metal film, for example. However, theinvention is not limited thereto, and in another exemplary embodiment,the substrate 210 may also be a rigid display substrate.

The organic light emitting element layer 220 is disposed on thesubstrate 210. Although not illustrated, a buffer layer may be providedbetween the substrate 210 and the organic light emitting element layer220 to flatten an upper surface of the substrate 210 and block thepenetration of impurities into the organic light emitting element layer220.

The organic light emitting element layer 220 may include a plurality ofthin-film transistors (“TFTs”) and a plurality of organic light emittingdiodes (“OLEDs”). Each of the OLEDs may be a structure in which ananode, an organic light emitting layer, and a cathode are sequentiallystacked. Source/drain electrodes of some of the TFTs may be electricallyconnected to the anodes of the OLEDs.

The encapsulation layer 230 is provided over the entire surface of thesubstrate 210 so as to cover the organic light emitting element layer220. The encapsulation layer 230 is provided to protect the OLEDs fromexternal moisture, oxygen, or the like. The encapsulation layer 230 mayinclude multiple layers or a single layer including an insulatinginorganic material. In an exemplary embodiment, the inorganic materialmay be a metal oxide or a metal nitride. Specifically, the inorganicmaterial may be silicon oxide (SiO₂), silicon nitride (SiNx), siliconoxynitride (SiON), aluminum oxide (Al₂O₃), titanium oxide (TiO₂),tantalum oxide (Ta₂O₅), hafnium oxide (HfO₂), or zinc oxide (ZrO₂), forexample. The encapsulation layer 230 may form an encapsulation structurein which a thin film including an organic material and a thin filmincluding an inorganic material are further alternately stacked on athin film including an insulating organic material.

According to the exemplary embodiment, the organic light emittingdisplay device 20 employing the flexible display substrate 210 and theencapsulation layer 230 made flexible by being provided as a thin filmmay be bent, folded, or unfolded.

The touch sensing layer 240 may be disposed on the encapsulation layer230. The touch sensing layer 240 may be an electrostatic capacitive typetouch screen panel in an exemplary embodiment. However, the invention isnot limited thereto, and in another exemplary embodiment, the touchsensing layer 240 may also be any one of resistive type, electromagnetictype, surface acoustic wave (“SAW”) type, and infrared type touch screenpanels. Like the flexible display substrate 210, the touch sensing layer240 uses a flexible material that may be bent or folded. However, theinvention is not limited thereto, and in another exemplary embodiment,the touch sensing layer 240 may be omitted.

The cover window 250 is disposed on the touch sensing layer 240.Although not illustrated, the cover window 250 may be attached to thetouch sensing layer 240 using an OCA or optically clear resin (“OCR”)disposed between the cover window 250 and the touch sensing layer 240.

The cover window 250 may include glass having a high modulus. Themodulus of the cover window 250 may be about 50 GPa or more in anexemplary embodiment. The cover window 250 having a high modulus mayhelp prevent buckling from occurring easily even when the adhesive laver110 of the protection film 10 attached to the cover window 250 becomesthick.

In order to protect itself from damages such as cracks and flaws, thecover window 250 may include a window film 251 and a coating layer 252disposed on a surface of the window film 251 to lower the probability ofa damage of the window film 251. The window film 251 may include atransparent plastic film. In an exemplary embodiment, the plastic filmmay include, but is not limited to, polyethylene terephthalate,polymethyl methacrylate, polycarbonate, or polyimide, for example.

The material of the cover window 250 is not limited to theabove-mentioned glass and, in another exemplary embodiment, the materialof the cover window 250 may be a flexible material that enables theorganic light emitting display device 20 to be bent, folded, andunfolded.

Light emitted from the organic light emitting element layer 220 may beseen by a user through the cover window 250. The protection film 10 maybe attached onto the cover window 250 which is the light emittingsurface.

The cover window 250 of the organic light emitting display device 20described above may be easily damaged by an external impact even when itincludes the coating layer 252. Therefore, the protection film 10 isattached onto the cover window 250 so as to prevent the organic lightemitting display device 20 from being easily damaged by an externalimpact.

Next, the bonding relationship between the base layer 120 and theadhesive layer 110 will be described.

FIG. 4 is a cross-sectional view illustrating a process in which theorganic light emitting display device 20 to which the protection film 10of in FIG. 1 has been attached is folded. FIG. 5 is a cross-sectionalview illustrating a process in which the organic light emitting displaydevice 20 to which the protection film 10 of FIG. 1 has been attached isunfolded. FIG. 6 is a graph illustrating the amount of tensile stressaccording to the strain of the adhesive layer 110 in the A region whenthe processes of FIGS. 4 and 5 are repeated. FIG. 7 is a graphillustrating the strain of the adhesive layer 110 according to thethickness of the adhesive layer 110 for each thickness of the base layer120. FIG. 8 is a cross-sectional view illustrating, as a comparativeexample, a folded protection film 10_1 to which an adhesive layer 110_1having a thickness exceeding the maximum usable thickness has beenapplied.

Referring to FIGS. 4 and 5 , as described above, the organic lightemitting display device 20 may be a foldable display device 20, and theprotection film 10 according to the exemplary embodiment may be attachedonto the foldable display device 20. The organic light emitting displaydevice 20 may be folded and unfolded in the A region. When the organiclight emitting display device 20 is folded and unfolded in the A region,the protection film 10 attached onto the organic light emitting displaydevice 20 may also be folded and unfolded in the A region, like theorganic light emitting display device 20.

A direction in which the organic light emitting display device 20 isfolded may be a direction in which the light emitting surface facesinward. That is, when the protection film 10 is attached onto the coverwindow 250 of the organic light emitting display device 20, the organiclight emitting display device 20 may be folded such that the radius ofcurvature becomes greater in the order of the base layer 120, theadhesive layer 110, the cover window 250 and the substrate 210 in the Aregion.

When the protection film 10 is folded to the maximum, the radius ofcurvature of the base layer 120 may be about 0.5 R or more, for example.In an exemplary embodiment, the radius of curvature of the base layer120 may be about 0.5 R to about 1.5 R, for example. Here, the radius ofcurvature of the base layer 120 may be the radius of curvature of theadhesive surface where the base layer 120 and the adhesive layer 110 areattached.

When the protection film 10 is folded to the maximum, the side surfacesof the adhesive layer 110 may be inclined due to tensile stress andcompressive stress existing in the adhesive laver 110. In this case,under the condition that the radius of curvature of the adhesive layer110 is 0.5 R or more, an angle θ defined by a tangent to a side surfaceof the base layer 120 and an inclined surface of the adhesive layer 110may be 2 degrees or more, for example. In an exemplary embodiment, theangle θ may be 3 degrees to 25 degrees, for example.

Referring to FIG. 6 , the illustrated graph represents a firstexperimental example and shows the tensile stress in the adhesive layer110 and the tensile strain of the adhesive layer 110 in a case where theorganic light emitting display device 20 to which the protection film 10has been attached is repeatedly folded and unfolded as illustrated inFIGS. 4 and 5 . Here, the tensile strain is the ratio of the increase inlength caused by applied tensile load to the original length.

Referring to a solid line graph (cyclic test) of FIG. 6 , when no forceis applied to the protection film 10 (when the protection film 10 isattached flat as in FIG. 3 ), tensile stress applied to the adhesivelayer 110 may be close to 0 MPa. When the protection film 10 starts tobe folded due to an external force as illustrated in FIG. 4 , thetensile strain may increase, and the tensile stress of the adhesivelayer 110 may increase. When the protection film 10 starts to beunfolded due to an external force as illustrated in FIG. 5 , the tensilestrain may increase, and the tensile stress of the adhesive layer 110may decrease. In the case of FIG. 5 , the tensile strain is reducedbecause the protection film 10 returns to its original shape as it isunfolded. At this time, since the shape of the adhesive layer 110 ispartially restored, the tensile strain is partially reduced togetherwith the tensile stress. However, in the case of FIG. 5 , the tensilestrain of the adhesive layer 110 may not be restored to 0% becausedeformation exceeding a restoration critical point has occurred.Although not illustrated in the drawing, when the folding and unfoldingof the protection film 10 are repeated, the tensile strain may becomeclose to a maximum tensile strain.

Here, when the protection film 10 exceeds the maximum tensile strain,the adhesive layer 110 may buckle.

Referring to a dotted line graph (tensile test) of FIG. 6 , when theprocess of folding and unfolding the protection film 10 once is referredto as a cycle, maximum tensile stress per cycle may exist. Theprotection film 10 may include the maximum tensile stress per cycle whenit is folded to the maximum. The maximum tensile stress per cycle mayincrease sharply until it reaches about 200 MPa, but may increasegradually from 200 MPa or more, for example. That is, the rate of changein the maximum tensile stress per cycle may start to be reduced fromaround 200 MPa, for example.

FIG. 6 is an exemplary graph for explaining the change in the tensilestrain of the protection film 10 and the tensile stress in theprotection film 10 when the process of folding and unfolding theprotection film 10 is repeated. The tensile strain of the protectionfilm 10 and the tensile stress inside the protection film 10 are notlimited to values indicated by this graph in all experimental examples.In an exemplary embodiment, the rate of change in the tensile stressinside the protection film 10 may start to be reduced from around avalue other than about 200 MPa, and the tensile strain of the protectionfilm 10 may increase or decrease at a larger rate of change or mayincrease or decrease at a smaller rate of change, for example.

Referring to FIG. 7 , a number of experiments were conducted to identifythe usable thickness of the adhesive layer 110 and the maximumcompressive strain of the adhesive layer 110 according to the modulusand thickness of the base layer 120 under a high temperature conditionof about 65° C. when the base layer 120 had a radius of curvature of 1.5R. The graph of experimental results illustrated in FIG. 7 shows themaximum compressive strain of the adhesive layer 110 after the organiclight emitting display device 20 to which the protection film 10 hasbeen attached is folded and unfolded more than 1000 times as illustratedin FIGS. 4 to 6 . The compressive strain is a strain according toexternal compressive stress and may have a sign opposite to that of thetensile strain of FIG. 6 . In the experiments, an experimenter attachedadhesive layers 110 having thicknesses of about 25 μm, about 35 μm,about 50 μm, about 75 μm and about 100 μm to the base layer 120 in orderto identify the maximum compressive strain of each adhesive layer 110and whether each adhesive layer 110 buckled. In the graph of FIG. 7 ,the horizontal axis represents the thickness of the adhesive layer 110,and the vertical axis represents the maximum compressive strain of theadhesive layer 110. For ease of description, the maximum compressivestrain will be described based on an absolute value.

A protection film 10_2 according to a second experimental exampleincludes a base layer 120 having a thickness of about 25 μm and amodulus of about 4.15 GPa. Referring to the second experimental example,as the thickness of the adhesive layer 110 increases, the maximumcompressive strain of the adhesive layer 110 increases from about 0.51%at a thickness of 25 μm of the adhesive layer 110. However, when thethickness of the adhesive layer 110 was about 75 μm and about 100 μm,the adhesive layer 110 buckled.

A protection film 10_3 according to a third experimental exampleincludes a base layer 120 having a thickness of about 35 μm and amodulus of about 4.15 GPa. Referring to the third experimental example,as the thickness of the adhesive layer 110 increases, the maximumcompressive strain of the adhesive layer 110 increases from about 0.50%at a thickness of 25 μm of the adhesive layer 110. In the thirdexperimental example, the maximum compressive strain of the adhesivelayer 110 has a smaller value at each thickness of the adhesive layer110 than in the second experimental example. When the thickness of theadhesive layer 110 was about 75 μm and about 100 μm, the adhesive layer110 buckled.

A protection film 10_4 according to a fourth experimental exampleincludes a base layer 120 having a thickness of about 40 μm and amodulus of about 4.15 GPa. Referring to the fourth experimental example,as the thickness of the adhesive layer 110 increases, the maximumcompressive strain of the adhesive layer 110 increases from about 0.49%at a thickness of 25 μm of the adhesive layer 110. In the fourthexperimental example, the maximum compressive strain of the adhesivelayer 110 has a smaller value at each thickness of the adhesive layer110 than in the third experimental example. When the thickness of theadhesive layer 110 was about 100 μm, the adhesive layer 110 buckled.

A protection film 10_5 according to a fifth experimental exampleincludes a base layer 120 having a thickness of about 50 μm and amodulus of about 4.15 GPa Referring to the fifth experimental example,as the thickness of the adhesive layer 110 increases, the maximumcompressive strain of the adhesive layer 110 decreases from about 0.49%at a thickness of 25 μm of the adhesive layer 110 and then increases. Inthe fifth experimental example, the maximum compressive strain of theadhesive layer 110 has a smaller value at each thickness of the adhesivelayer 110 than in the fourth experimental example. In all cases wherethe thickness of the adhesive layer 110 was about 25 μm, about 35 μm,about 50 μm, about 75 μm and about 100 μm, buckling did not occur.

A protection film 10_6 according to a sixth experimental exampleincludes a base layer 120 having a thickness of about 65 μm and amodulus of about 4.15 GPa Referring to the sixth experiment example, asthe thickness of the adhesive layer 110 increases, the maximumcompressive strain of the adhesive layer 110 decreases from about 0.50%at a thickness of 25 μm of the adhesive layer 110 and then increases. Inthe sixth experimental example, the maximum compressive strain of theadhesive layer 110 does not always have a smaller value at eachthickness of the adhesive layer 110 than in the fifth experimentalexample, but has higher values at some small thicknesses of the adhesivelayer 110. In all cases where the thickness of the adhesive layer 110was about 25 μm, about 35 μm, about 50 μm, about 75 μm and about 100 μm,buckling did not occur.

A protection film 10_7 according to a seventh experimental exampleincludes a base layer 120 having a thickness of about 75 μm and amodulus of about 4.15 GPa. Referring to the seventh experimentalexample, as the thickness of the adhesive layer 110 increases, themaximum compressive strain of the adhesive layer 110 decreases fromabout 0.51% at a thickness of 25 μm of the adhesive layer 110 and thenincreases. In the seventh experimental example, the maximum compressivestrain of the adhesive layer 110 does not always have a smaller value ateach thickness of the adhesive layer 110 than in the sixth experimentalexample, but has higher values at some small thicknesses of the adhesivelayer 110. In all cases where the thickness of the adhesive layer 110was about 25 μm, about 35 μm, about 50 μm, about 75 μm and about 100 μm,buckling did not occur.

A protection film 10_8 according to an eighth experimental exampleincludes a base layer 120 having a thickness of about 25 μm and amodulus of about 6.0 GPa. Referring to the eighth experimental example,as the thickness of the adhesive layer 110 increases, the maximumcompressive strain of the adhesive layer 110 increases from about 0.445%at a thickness of 25 μm of the adhesive layer 110. In the eighthexperimental example, the maximum compressive strain of the adhesivelayer 110 has a smaller value at each thickness of the adhesive layer110 than in the seventh experimental example. However, when thethickness of the adhesive layer 110 was about 75 μm and about 100 μm,the adhesive layer 110 buckled.

A protection film 10_9 according to a ninth experimental exampleincludes a base layer 120 having a thickness of about 35 μm and amodulus of about 6.0 GPa. Referring to the ninth experimental example,as the thickness of the adhesive layer 110 increases, the maximumcompressive strain of the adhesive layer 110 increases from about 0.44%at a thickness of 25 μm of the adhesive layer 110. In the ninthexperimental example, the maximum compressive strain of the adhesivelayer 110 has a smaller value at each thickness of the adhesive layer110 than in the eighth experimental example. However, when the thicknessof the adhesive layer 110 was about 75 μm and about 100 μm, the adhesivelayer 110 buckled.

A protection film 10_10 according to a tenth experimental exampleincludes a base layer 120 having a thickness of about 40 μm and amodulus of about 6.0 GPa. Referring to the tenth experimental example,as the thickness of the adhesive layer 110 increases, the maximumcompressive strain of the adhesive layer 110 decreases from about 0.43%at a thickness of 25 μm of the adhesive layer 110 and then increases. Inthe tenth experimental example, the maximum compressive strain of theadhesive layer 110 has a smaller value at each thickness of the adhesivelayer 110 than in the ninth experimental example. In all cases where thethickness of the adhesive layer 110 was about 25 μm, about 35 μm, about50 μm, about 75 μm and about 100 μm, buckling did not occur.

A protection film 10_11 according to an eleventh experimental exampleincludes a base layer 120 having a thickness of about 50 μm and amodulus of about 6.0 GPa. Referring to the eleventh experimentalexample, as the thickness of the adhesive layer 110 increases, themaximum compressive strain of the adhesive layer 110 decreases fromabout 0.43% at a thickness of 25 μm of the adhesive layer 110 and thenincreases. In the eleventh experimental example, the maximum compressivestrain of the adhesive layer 110 has a smaller value at each thicknessof the adhesive layer 110 than in the tenth experimental example. In allcases where the thickness of the adhesive layer 110 was about 25 μm,about 35 μm, about 50 μm, about 75 μm and about 100 μm, buckling did notoccur.

A protection film 10_12 according to a twelfth experimental exampleincludes a base layer 120 having a thickness of about 65 μm and amodulus of about 6.0 GPa. Referring to the twelfth experimental example,as the thickness of the adhesive layer 110 increases, the maximumcompressive strain of the adhesive layer 110 decreases from about 0.44%at a thickness of 25 μm of the adhesive layer 110 and then increases. Inthe twelfth experimental example, the maximum compressive strain of theadhesive layer 110 does not always have a smaller value at eachthickness of the adhesive layer 110 than in the eleventh experimentalexample, but has higher values at some small thicknesses of the adhesivelayer 110. In all cases where the thickness of the adhesive layer 110was about 25 μm, about 35 μm, about 50 μm, about 75 μm and about 100 μm,buckling did not occur.

A protection film 10_13 according to a thirteenth experimental exampleincludes a base layer 120 having a thickness of about 25 μm and amodulus of about 9.0 GPa. Referring to the thirteenth experimentalexample, as the thickness of the adhesive layer 110 increases, themaximum compressive strain of the adhesive layer 110 increases fromabout 0.38% at a thickness of 25 μm of the adhesive layer 110. In thethirteenth experimental example, the maximum compressive strain of theadhesive layer 110 has a smaller value at each thickness of the adhesivelayer 110 than in the twelfth experimental example. However, when thethickness of the adhesive layer 110 was about 75 μm and about 100 μm,the adhesive layer 110 buckled.

A protection film 10_14 according to a fourteenth experimental exampleincludes a base layer 120 having a thickness of about 35 μm and amodulus of about 9.0 GPa. Referring to the fourteenth experimentalexample, as the thickness of the adhesive layer 110 increases, themaximum compressive strain of the adhesive layer 110 increases fromabout 0.37% at a thickness of 25 μm of the adhesive layer 110. In thefourteenth experimental example, the maximum compressive strain of theadhesive layer 110 has a smaller value at each thickness of the adhesivelayer 110 than in the thirteenth experimental example. However, when thethickness of the adhesive layer 110 was about 100 μm, the adhesive layer110 buckled.

A protection film 10_15 according to a fifteenth experimental exampleincludes a base layer 120 having a thickness of about 40 μm and amodulus of about 9.0 GPa. Referring to the fifteenth experimentalexample, as the thickness of the adhesive layer 110 increases, themaximum compressive strain of the adhesive layer 110 decreases fromabout 0.36% at a thickness of 25 μm of the adhesive layer 110 and thenincreases. In the fifteenth experimental example, the maximumcompressive strain of the adhesive layer 110 has a smaller value at eachthickness of the adhesive layer 110 than in the fourteenth experimentalexample. In all cases where the thickness of the adhesive layer 110 wasabout 25 μm, about 35 μm, about 50 μm, about 75 μm and about 100 μm,buckling did not occur.

In addition to the above experimental examples, various otherexperiments show that the maximum compressive strain of the adhesivelayer 110 substantially decreases as the modulus of the base layer 120increases and substantially decreases as the thickness of the adhesivelayer 110 decreases.

Experiments were conducted to identify the relationship between themodulus and thickness of the base layer 120 and the maximum usablethickness of the adhesive layer 110. In the experiments, as in theabove-described experimental examples, values were measured under a hightemperature condition of about 65° C. when the radius of curvature ofthe base layer 120 was about 1.5 R. The results of the experiments areshown in Table 1 below. The values shown in Table 1 are approximatevalues, and some minor errors may exist.

TABLE 1 Maximum usable thickness of adhesive layer, z [μm] Modulus ofbase If x If x Thickness of base layer; when [GPa] = [GPa] = layer, y[μm] x [GPa] = 4.15, 6.0, 9.0, 35  77  84  94 40  87  96 108 50 104 116131 65 124 139 158 75 135 151 173

When the base layer 120 had a thickness of about 35 μm and a modulus ofabout 4.15 GPa, the maximum usable thickness of the adhesive layer 110could be about 77 μm. When the base layer 120 had a thickness of about35 μm and a modulus of about 6.0 GPa, the maximum usable thickness ofthe adhesive layer 110 could be about 84 μm. When the base layer 120 hada thickness of about 35 μm and a modulus of about 9.0 GPa, the maximumusable thickness of the adhesive layer 110 could be about 94 μm. Whenthe base layer 120 had a thickness of about 40 μm and a modulus of about4.15 GPa, the maximum usable thickness of the adhesive layer 110 couldbe about 87 μm. When the base layer 120 had a thickness of about 40 μmand a modulus of about 6.0 GPa, the maximum usable thickness of theadhesive layer 110 could be about 96 μm. When the base layer 120 had athickness of about 40 μm and a modulus of about 9.0 GPa, the maximumusable thickness of the adhesive layer 110 could be about 108 μm. Whenthe base layer 120 had a thickness of about 50 μm and a modulus of about4.15 GPa, the maximum usable thickness of the adhesive layer 110 couldbe about 104 μm. When the base layer 120 had a thickness of about 50 μmand a modulus of about 6.0 GPa, the maximum usable thickness of theadhesive layer 110 could be about 116 μm. When the base layer 120 had athickness of about 50 μm and a modulus of about 9.0 GPa, the maximumusable thickness of the adhesive layer 110 could be about 131 μm. Whenthe base layer 120 had a thickness of about 65 μm and a modulus of about4.15 GPa, the maximum usable thickness of the adhesive layer 110 couldbe about 124 μm. When the base layer 120 had a thickness of about 65 μmand a modulus of about 6.0 GPa, the maximum usable thickness of theadhesive layer 110 could be about 139 μm. When the base layer 120 had athickness of about 65 μm and a modulus of about 9.0 GPa, the maximumusable thickness of the adhesive layer 110 could be about 158 μm. Whenthe base layer 120 had a thickness of about 75 μm and a modulus of about4.15 GPa, the maximum usable thickness of the adhesive layer 110 couldbe about 135 μm. When the base layer 120 had a thickness of about 75 μmand a modulus of about 6.0 GPa, the maximum usable thickness of theadhesive layer 110 could be about 151 μm. When the base layer 120 had athickness of about 75 μm and a modulus of about 9.0 GPa, the maximumusable thickness of the adhesive layer 110 could be about 173 μm.

In addition to the experimental examples of Table 1, various otherexperiments showed that the maximum usable thickness of the adhesivelayer 110 according to the modulus of the base layer 120 and thethickness of the base layer 120 substantially satisfied Equation 3below. In addition, the relationship between the base layer 120 and theadhesive layer 110 satisfied Equation 3 when the radius of curvature ofthe base layer 120 was about 0.5 R or more, the thickness of the baselayer 120 was about 25 μm to about 75 μm, the modulus of the base layer120 was about 2 GPa to about 9 GPa, and the temperature was about −40°C. to about 65° C.

$\begin{matrix}{z = {{\left( {{5.1x} + 57.4} \right) \cdot {\ln(y)}} - {\left( {{14.7x} + 140.5} \right).}}} & (3)\end{matrix}$

In Table 1 and Equation 3 above, x is the modulus value of the baselayer 120 measured in GPa, y is the thickness value of the base layer120 measured in μm, and z is the maximum usable thickness of theadhesive layer 110 measured in μm.

The maximum usable thickness z1 of the adhesive layer 110 of FIG. 1 maybe a value (z=z1) calculated by applying Equation 3 to the thickness(y=y1) of the base layer 120 at a modulus value (x=x1) of the base layer120. That is, the relationship between z1 and y1 may satisfy Equation 4below.

$\begin{matrix}{z_{1} = {{\left( {{5.1x_{1}} + 57.4} \right) \cdot {\ln\left( y_{1} \right)}} - {\left( {{14.7x_{1}} + 140.5} \right).}}} & (4)\end{matrix}$

In the case of the protection film 10 according to the exemplaryembodiment of FIG. 1 , z1 satisfying Equation 4 corresponds to themaximum usable thickness of the adhesive layer 110. Therefore, when theadhesive layer 110 of the protection film 10 has a thickness of z1 orless, buckling may not occur even when the protection film 10 isrepeatedly folded and unfolded more than 1000 times, for example.

However, referring to FIG. 8 as a comparative example, the protectionfilm 10_1 may include the adhesive layer 110_1 having a thicknessexceeding z1 that satisfies Equation 4. When the protection film 10_1 isrepeatedly folded and unfolded more than 1000 times, for example,buckling of the adhesive layer 110_1 may occur in a folding andunfolding region. The buckling may occur mostly near the boundary of abent portion. Here, the buckling may occur not only near the boundary onone side of the bent portion as illustrated in the drawing, but alsonear the boundary on the other side of the bent portion. However, sincethe buckling does not occur when the protection film 10_1 is used in aflexible display device or a rigid display device instead of thefoldable organic light emitting display device 20, it is possible toprevent the organic light emitting display device 20 from being damaged.

Next, the impact resistance performance of the organic light emittingdisplay device 20 according to the characteristics of the base layer 120and the thickness of the adhesive layer 110 will be described.

After protection films 10 according to sixteenth through nineteenthexperimental examples were attached to the organic light emittingdisplay device 20, a DuPont impact test and a pen drop test wereconducted. In the DuPont impact test, a precision weight of 30 gram (g)was dropped to measure a height in terms of centimeters that causedbright dots to be provided on the organic light emitting display device20. In the pen drop test, a height that caused the cover window 250 ofthe organic light emitting display device 20 to be broken was measuredusing a BIC ball pen having a weight of about 5.8 g and distributed byLazy Society Co., Ltd. In a comparative example, the DuPont impact testand the pen drop test were conducted on the organic light emittingdisplay device 20 without the protection film 10. The experimentalresults are shown in Table 2 below. The values shown in Table 2 areapproximate values, and some minor errors may exist.

TABLE 2 Sixteenth Seventeenth Eighteenth Nineteenth Comparativeexperimental experimental experimental experimental example exampleexample example example DuPont Bright dots at Bright dots at Bright dotsat Bright dots at Bright dots at impact test 2 cm  5 cm  7 cm  3 cm 4 cmPen drop Broken at Broken at Broken at Broken at Broken at test 1 cm 13cm 16 cm 16 cm 8 cm

As described above, the comparative example was conducted withoutattaching the protection film 10 to the organic light emitting displaydevice 20. Here, in the sixteenth experimental example, a protectionfilm 10 including a base layer 120 having a thickness of about 40 μm anda modulus of about 4.15 GPa and an adhesive layer 110 having a thicknessof about 50 μm were attached. In the seventeenth experimental example, aprotection film 10 including a base layer 120 having a thickness ofabout 40 μm and a modulus of about 4.15 GPa and an adhesive layer 110having a thickness of about 100 μm were attached. In the eighteenthexperimental example, a protection film 10 including a base layer 120having a thickness of about 50 μm and a modulus of about 4.15 GPa and anadhesive layer 110 having a thickness of about 50 μm were attached. Inthe nineteenth experimental example, a protection film 10 including abase layer 120 having a thickness of about 25 μm and a modulus of about1.5 GPa and an adhesive layer 110 having a thickness of about 50 μm wereattached.

According to the above experiments, in the case of the DuPont impacttest, the height that caused bright dots to be provided increased as thethickness of the adhesive layer 110 increased. In the case of the pendrop test, the cover window 250 of the organic light emitting displaydevice 20 was very vulnerable when the protection film 10 was notattached, but the height that caused the cover window 250 to be brokenincreased sharply as the modulus of the base layer 120 and the thicknessof the protection film 10 increased.

Therefore, a damage to the organic light emitting display device 20 dueto an external impact may be reduced when the protection film 10includes an adhesive layer 110 having a maximum thickness that does notcause buckling according to the modulus and thickness of the base layer120.

Protection films according to other exemplary embodiments will now bedescribed. In the following embodiments, a redundant description ofelements and features identical to those described above with referenceto FIGS. 1 through 8 will be omitted. In addition, the same referencenumerals will be used for the same elements as those described abovewith reference to FIGS. 1 through 3 .

FIG. 9 is a cross-sectional view of a protection film 11 according to anexemplary embodiment.

Referring to FIG. 9 , the protection film 11 is different from theprotection film 10 of FIG. 1 in that a functional layer 130 is furtherattached onto a base layer 120.

The protection film 11 may include an adhesive layer 110, the base layer120, and the functional layer 130. The base layer 120 may be disposed onthe adhesive layer 110, and the functional layer 130 may be disposed onthe base layer 120.

The functional layer 130 may include any one or more of ananti-fingerprint coating layer, an anti-fouling coating layer, ananti-reflection coating layer, an anti-glare coating layer, ahard-coating layer, and a self-restoring layer. The illustratedexemplary embodiment to be described below merely explains a structurein which the functional layer 130 includes a hard-coating layer 131, ananti-fingerprint coating layer 132 and a self-restoring layer 133 and isnot limited to this structure.

The hard-coating layer 131 may be disposed on the base layer 120. Thehard-coating layer 131 disposed on the base layer 120 may reduce thedistortion or lifting phenomenon of the protection film 11 under severeconditions such as high temperature or high temperature and highhumidity, thereby improving reliability.

Although not illustrated, the hard-coating layer 131 may include anorganic layer and an organic-inorganic composite layer. Here, theorganic layer may include an acrylate-based compound. In an exemplaryembodiment, the organic layer may include urethane acrylate, forexample. The organic layer may be disposed between the base layer 120and the organic-inorganic composite layer to serve as a stress bufferlayer. In an exemplary embodiment, the organic layer may have athickness of about 20 μm or less, for example.

An organic material in the organic-inorganic composite layer may includeat least one or a combination of an acrylate-based compound, apolyurethane-based compound, and an epoxy-based compound. In anexemplary embodiment, first and second organic-inorganic compositelayers may include urethane acrylate, for example. In an exemplaryembodiment, an inorganic material in the organic-inorganic compositelayer may be at least any one of silicon oxide (SiO₂), zirconium oxide(ZrO₂), aluminum oxide (Al₂O₃), tantalum oxide (Ta₂O₅), niobium oxide(Nb₂O₅, NbO₂), and glass bead, for example.

The inorganic material may be provided in the form of a single kind ofinorganic oxide listed or a combination of these materials. In addition,the inorganic material may be provided in various forms to form theorganic-inorganic composite layer. In an exemplary embodiment, siliconoxide may be provided in the form of SiO₂ particles, a SiO₂ sol in whichSiO₂ particles are dispersed in a colloidal state, or SiO₂ having ahollow shape, for example.

In the organic-inorganic composite layer, an acrylate compound (i.e., anorganic material) and inorganic particles may be mixed in a weight ratioof 5:5 to 8:2, for example. By including both the acrylate compound andthe inorganic particles, the organic-inorganic composite layer may formthe hard-coating layer 131 that has improved surface hardness and is noteasily broken due to its ability to absorb external shock.

The anti-fingerprint coating layer 132 may be disposed on thehard-coating layer 131. In an exemplary embodiment, the anti-fingerprintcoating layer 132 is provided by providing a coating material includingperfluoropolyether using a spray coating method and thermally curing thecoating material at about 60° C. for about 60 minutes, for example. Inan exemplary embodiment, the provided anti-fingerprint coating layer 132may have a thickness of about 50 μm, for example. The anti-fingerprintcoating layer 132 may be provided using not only the above-describedmethod, but also using various methods.

The self-restoring layer 133 may be disposed on the anti-fingerprintcoating layer 132. The self-restoring layer 133 is provided using aself-restoring composition including aromatic urethane acrylate resins.In the self-restoring layer 133, the urethane acrylate resins may beincluded in a ladder structure that may be supported by an aromaticgroup, a heteroaromatic group, or both. The aromatic urethane acrylateresins may be urethane acrylate resins having 2 to 5 functional groupson average, may be provided by reacting a polymerizable compositionincluding acrylate, which includes a hydroxyl group, and an isocyanatecompound, and at least one of the acrylate including the hydroxyl groupand the isocyanate compound may include an aromatic group, aheteroaromatic group, or both.

In an exemplary embodiment, the thickness of the self-restoring layer133 may be about 15 μm to about 40 μm, for example. By having athickness within the above range, the self-restoring layer 133 mayexhibit sufficient bending and self-restoring properties withoutexcessively increasing the total thickness of the protection film 11.Thus, the self-restoring layer 133 may have uniform performance over along period of time.

As in the exemplary embodiment of FIG. 1 , in the protection film 11including the functional laver 130, the maximum usable thickness of theadhesive layer 110 may be applied according to Equation 3 regarding therelationship between the base layer 120 and the adhesive layer 110 whenthe radius of curvature of the base laver 120 is about 0.5 R or more,the thickness of the base laver 120 is about 25 μm to about 75 μm, themodulus of the base laver 120 is about 2 GPa to about 9 GPa, and thetemperature is about −40° C. to about 65° C., for example. In anexemplary embodiment, the maximum usable thickness of the adhesive layer110 of the protection film 11 according to the illustrated exemplaryembodiment may satisfy Equation 5 below.

$\begin{matrix}{{z_{2} = {{\left( {{5.1x_{1}} + 57.4} \right) \cdot {\ln\left( y_{2} \right)}} - \left( {{14.7x_{2}} + 140.5} \right)}},} & (5)\end{matrix}$where x2 is the modulus of the base layer 120. Here, y2 is a valueobtained by adding not only the thickness of the base layer 120 but alsothe thickness of the functional layer 130. That is, y2 may be the totalthickness of all layers stacked on the adhesive layer 110. In anexemplary embodiment, since all layers stacked on the adhesive layer 110include only the base layer 120 in FIG. 1 , y1 may be the thickness ofthe base layer 120, for example. In the illustrated exemplaryembodiment, since all layers stacked on the adhesive layer 110 includethe base layer 120 and the functional layer 130, 2 may be the sum of thethickness of the base layer 120 and the thickness of the functionallayer 130.

When the thickness of the adhesive layer 110 is z2 or less, buckling maynot occur in the protection film 11.

As in the exemplary embodiment of FIG. 1 , a damage to the organic lightemitting display device 20 due to an external impact may be reduced whenthe protection film 11 including the adhesive layer 110 of the maximumusable thickness is attached to the organic light emitting displaydevice 20.

FIG. 10 is a cross-sectional view of a protection film 12 according toan exemplary embodiment. Referring to FIG. 10 , the protection film 12according to the illustrated exemplary embodiment is different from theprotection film 11 of FIG. 9 in that it further includes a primer layer141 disposed between a base layer 120 and a functional layer 130. Theprimer layer 141 may be an adhesion-assisting layer for enhancing theadhesion between the base layer 120 and a hard-coating layer 131.

The protection film 12 of the illustrated exemplary embodiment mayfurther include the primer layer 141 between the functional layer 130and the base layer 120. Specifically, the primer layer 141 may bedisposed between the base layer 120 and the hard-coating layer 131. Inan exemplary embodiment, the primer layer 141 may include a silanecoupling agent and isocyanate, for example.

In an exemplary embodiment, the primer layer 141 may have a thickness of10 nanometers (nm) to 30 nm, for example. When the primer layer 141 isprovided thinner than 10 nm, its function as an adhesion-assisting layermay deteriorate, thus weakening the adhesion to the functional layer130. In addition, when the primer layer 141 is provided thicker than 30nm, a haze phenomenon may occur, thus degrading optical characteristicsof the primer layer 141.

As in the exemplary embodiment of FIG. 1 , in the protection film 12including the primer layer 141, the maximum usable thickness of anadhesive layer 110 may be applied according to Equation 3 regarding therelationship between the base layer 120 and the adhesive layer 110 whenthe radius of curvature of the base layer 120 is about 0.5 R or more,the thickness of the base layer 120 is about 25 μm to about 75 μm, themodulus of the base layer 120 is about 2 GPa to about 9 GPa, and thetemperature is about −40° C. to about 65° C., for example. In anexemplary embodiment, the maximum usable thickness of the adhesive layer110 of the protection film 12 according to the illustrated exemplaryembodiment may satisfy Equation 6 below.

$\begin{matrix}{{z_{3} = {{\left( {{5.1x_{3}} + 57.4} \right) \cdot {\ln\left( y_{3} \right)}} - \left( {{14.7x_{3}} + 140.5} \right)}},.} & (6)\end{matrix}$where x3 is the modulus of the base laver 120. Since y3 is the totalthickness of all layers stacked on the adhesive layer 110, it may be,for example, the sum of the thickness of the base layer 120, thethickness of the primer layer 141, and the thickness of the functionallaver 130.

When the thickness of the adhesive layer 110 is z3 or less, buckling maynot occur in the protection film 12.

As in the exemplary embodiment of FIG. 1 , a damage to the organic lightemitting display device 20 due to an external impact may be reduced whenthe protection film 12 including the adhesive layer 110 of the maximumusable thickness is attached to the organic light emitting displaydevice 20.

A protective film may have excellent durability for a long period oftime and protect an electronic device from the outside.

However, the effects of the invention is not restricted to the one setforth herein. The above and other effects of the exemplary embodimentswill become more apparent to one of daily skill in the art to which theexemplary embodiments pertain by referencing the claims.

What is claimed is:
 1. A display device comprising: a substrate; a lightemitting layer on the substrate; an encapsulation layer on the lightemitting layer; a touch sensing layer on the encapsulation layer; acover window on the touch sensing layer; and a protection film on thecover window, wherein the protection film includes a base layer and anadhesive layer on the base layer, the adhesive is disposed between thecover window and the base layer, the base layer has a modulus of about 2gigapascals to about 9 gigapascals, the base layer has a thickness ofabout 25 micrometers to 75 micrometers, the adhesive layer has a modulusof about 10 megapascals or less at a temperature of −20 degrees Celsiusor lower, and the adhesive layer has a thickness of 100 micrometers ormore.
 2. The display device of claim 1, wherein the adhesive layercomprises an acrylic-based adhesive.
 3. The display device of claim 1,wherein the encapsulation layer comprises a thin film including aninorganic material and a thin film including an organic material.
 4. Thedisplay device of claim 1, wherein the encapsulation layer comprises: afirst inorganic layer on the touch sensing layer; an organic layer onfirst inorganic layer; and a second inorganic layer on the organiclayer.
 5. The display device of claim 1, wherein the thickness of theadhesive layer satisfies Inequality (1): $\begin{matrix}{{z \leq {{\left( {{5.1x} + 57.4} \right) \cdot {\ln(y)}} - \left( {{14.7x} + 140.5} \right)}},} & (1)\end{matrix}$ where z is the thickness of the adhesive layer in terms ofmicrometers and equal to or greater than 100 micrometers, x is a modulusof the base layer in terms of gigapascals, and y is a total thickness ofthe protection film layer in terms of micrometers,(5.1x+57.4)·ln(y)−(14.7x+140.5) is greater than zero, and a temperatureis about −40° C. to about 65° C.
 6. A display device comprising: asubstrate; a light emitting layer on the substrate; an encapsulationlayer on the light emitting layer; a touch sensing layer on theencapsulation layer; a cover window on the touch sensing layer; and aprotection film on the cover window, wherein the protection filmcomprises a base layer, a hard-coating layer on a first surface of thebase layer, and an adhesive layer on a second surface of the base layer,the second surface facing the cover window, the base layer has a modulusof about 2 gigapascals to about 9 gigapascals, the base layer has athickness of about 25 micrometers to 75 micrometers, the adhesive layerhas a modulus of about 10 megapascals or less at a temperature of −20degrees Celsius or lower, and the adhesive layer has a thickness of 100micrometers or more.
 7. The display device of claim 6, wherein thehard-coating layer comprises an organic layer.
 8. The display device ofclaim 7, wherein the organic layer includes an acrylate-based compound.9. The display device of claim 7, further comprising anorganic-inorganic composite layer.
 10. The display device of claim 6,wherein the thickness of the adhesive layer satisfies Inequality (2):$\begin{matrix}{{z \leq {{\left( {{5.1x} + 57.4} \right) \cdot {\ln(y)}} - \left( {{14.7x} + {140\text{.5}}} \right)}},} & (2)\end{matrix}$ where z is the thickness of the adhesive layer in terms ofmicrometers and equal to or greater than 100 micrometers, x is a modulusof the base layer in terms of gigapascals, and y is a total thickness ofthe protection film layer in terms of micrometers,(5.1x+57.4)·ln(y)−(14.7x+140.5) is greater than zero, and a temperatureis about −40° C. to about 65° C.
 11. A display device comprising: adisplay panel; a window on the display panel; and a protection filmlayer on the window, wherein the protection film comprises a base layer,a first functional layer on a first surface of the base layer, and anadhesive layer on a second surface of the base layer, the second surfacefacing the window, wherein a thickness of the adhesive layer satisfiesInequality (3): $\begin{matrix}{{z \leq {{\left( {{5.1x} + 57.4} \right) \cdot {\ln(y)}} - \left( {{14.7x} + {140\text{.5}}} \right)}},} & (3)\end{matrix}$ where z is the thickness of the adhesive layer in terms ofmicrometers, x is a modulus of the base layer in terms of gigapascals,and y is a total thickness of the protection film layer in terms ofmicrometers, (5.1x+57.4)·ln(y)−(14.7x+140.5) is greater than zero, and atemperature is about −40° C. to about 65° C., the thickness of theadhesive layer is about 25 micrometers or more, and the protection filmfurther comprises a second functional layer on the first functionallayer.
 12. The display device of claim 11, wherein the first functionallayer comprises an organic layer including an acrylate-based compound.13. The display device of claim 12, wherein the first functional layerfurther comprises an organic-inorganic composite layer.
 14. The displaydevice of claim 11, wherein the first functional layer is a hard-coatinglayer and the second functional layer is an anti-fingerprint coatinglayer.
 15. The display device of claim 11, wherein the protection filmfurther comprises a third functional layer, which is a self-restoringlayer, on the second functional layer.